The correct option is (b).
Explanation
The ozone layer is a region in the Earth's stratosphere that contains a high concentration of ozone ($O_3$) molecules. Its primary function is to absorb the majority of the Sun's harmful ultraviolet (UV) radiation, thereby protecting living organisms on Earth.
Statement-wise Analysis:
- Statement 1 is Incorrect. The ozone layer acts as a natural shield primarily against ultraviolet (UV) radiation, specifically UV-C and most UV-B. It does not act as a shield against infrared radiation. Infrared radiation is associated with heat energy; while ozone is a greenhouse gas and can absorb terrestrial infrared radiation, its role as a "shield" for incoming solar radiation refers to UV blockage.
- Statement 2 is Correct. Ozone absorbs ultraviolet radiation and undergoes photodissociation. When an ozone molecule absorbs UV energy, it splits into a dioxygen molecule ($O_2$) and a free oxygen atom ($O$). This chemical reaction consumes the energy of the UV radiation, preventing it from reaching the Earth's surface. This process is part of the Chapman cycle.
Key Takeaway:
The stratospheric ozone layer protects the Earth by absorbing harmful UV radiation through a continuous cycle of formation and destruction (Chapman cycle), whereas greenhouse gases are responsible for absorbing infrared radiation.